1. Field of the Invention
This invention relates to a novel process for the oil extraction from oil sand by using cyclodextrin.
2. Description of the Prior Art
Processes for the oil extraction from sand oil known in the art include a process for the oil extraction in situ comprising introducing steam at high temperature and high pressure into a layer containing oil sand, that is, a steam separation process, and a process for separating oil from open-air oil sand by using alkaline water at an elevated temperature. However, these processes have an economical disadvantage since these need a great amount of energy. Recently, a new oil extraction has been proposed which utilizes an inclusion capability of cyclodextrin and comprises including oil molecule contained in oil sand within a cavity of cyclodextrin molecule and then separating the inclusion compound to collect oil (see U.S. Pat. No. 4,255,249). This process is economically better than the steam separation process described above and comprises forming an inclusion compound of oil and cyclodextrin, separating the resulting, water-insoluble inclusion compound by any suitable technique such as centrifugation, and then introducing the separated inclusion compound into hot water or subjecting it to steam distillation to collect oil. Thus, the new process requires a troublesome operation and takes a relatively long time. The oil extraction yield of this process is not good (generally about 60%) due to the troublesome operation. As described above, the process using an inclusion compound mentioned above is not suitable for an industrial production in view of yield, time and cost.
The inventors of the present invention have paid attention to a special physical property of cyclodextrin, that is, the fact that cyclodextrin has surface activity and also accelerates separation between oil and sand contained in oil sand, and have studied a process of oil extraction from oil sand by using cyclodextrin. The inventors have found that the oil extraction from oil sand may easily and effectively be conducted by mixing oil sand, cyclodextrin in such an amount that the formation of the inclusion compound between oil and cyclodextrin may substantially be avoided, and water with one another to prepare a suspension and leaving the suspension to stand or centrifuging it to separate an oil layer (see U.S. Ser. No. 394,581).
The inventors of the present invention have further studied the process described above and have found that the addition of a hydrocarbon solvent such as kerosene to the suspension increases in the oil extraction yield, the addition of a flocculating agent such as benzylidene sorbitol results in the quick clarification of the water layer separated, which makes it possible to recycle the clarified water in the process, and that the continuous production of cyclodextrin by passing a starch solution through a column packed with an immobilized enzyme provides a continuous process comprising the production of cyclodextrin and the separation of oil. The present invention is a result of the discoveries mentioned above.